The Festival Speech Synthesis System is free software. Festival
is copyrighted by the University of Edinburgh and is distributed
under an X11 type licence.
There are no restrictions on its use (commercial or otherwise).
Note that voices and lexicons may have different restrictions though
complete free voices and lexicons are included in this distribution.

The licence is:

The Festival Speech Synthesis System
Centre for Speech Technology Research
University of Edinburgh, UK
Copyright (c) 1996-2014
All Rights Reserved.
Permission is hereby granted, free of charge, to use and distribute
this software and its documentation without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of this work, and to
permit persons to whom this work is furnished to do so, subject to
the following conditions:
1. The code must retain the above copyright notice, this list of
conditions and the following disclaimer.
2. Any modifications must be clearly marked as such.
3. Original authors' names are not deleted.
4. The authors' names are not used to endorse or promote products
derived from this software without specific prior written
permission.
THE UNIVERSITY OF EDINBURGH AND THE CONTRIBUTORS TO THIS WORK
DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT
SHALL THE UNIVERSITY OF EDINBURGH NOR THE CONTRIBUTORS BE LIABLE
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
THIS SOFTWARE.

Source distribution

Distributions

You will need both speech tools and festival source to compile
and also at least one lexicon and voice. These sources compile and
run under most Unix systems and Windows